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Using a d3 and a d3w together.....

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by KB4MNG, Dec 7, 2017 at 2:20 AM.

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  1. KB4MNG

    KB4MNG Ham Member QRZ Page

    I have a cushcraft d3 (10, 15, 20) and would like to have warc bands. The D3w covers the warcs. Could I mount these on the same support in an X fashion and feed with the same coax?
     
  2. W0AAT

    W0AAT XML Subscriber QRZ Page

    Would need the proper balun to match 25 ohms... but yes at 90 degrees offset they should play okay without to much interaction.
     
  3. KB4MNG

    KB4MNG Ham Member QRZ Page

    What balun would be required>

    thannks
     
  4. KW4TI

    KW4TI Ham Member QRZ Page

    If you're talking about putting the feeds of the two antennas in parallel, it is not necessarily the case that each is going to be 50 ohms at all frequencies and therefore putting them in parallel is going to give you 25 ohms. It is likely that the D3 presents a lower or higher impedance on the WARC bands than 50 ohms, and likewise the D3X presents a lower or higher impedance on the 10,15,20 m bands.

    It's hard to say what the total impedance will be with the two placed in parallel, but if the impedance of each of the antennas is significantly higher than the other antenna when its not resonant, the other antenna will dominate the parallel combination of the two antennas and the arrangement should work. Since those antennas are trapped dipoles, it seems to me that this arrangement might work, like a fan dipole works, if you make place the two antennas perpendicular to each other. I might give it a try, and I don't think you will need a balun to transform the impedance. Use low power of course to test!

    73,
    Dan
    KW4TI
     
  5. KB4MNG

    KB4MNG Ham Member QRZ Page

    How about if I installed a D3 on a support and added two 17 meter resonant legs in an inverted V fashion. Would this give me 17 and not effect the D3 bands? I would love to have 30 and that would be a motivation to try a d3w....
     
  6. WB2WIK

    WB2WIK Premium Subscriber QRZ Page

    You can wire them in parallel. The Z of the non-resonant antenna will be very high and it won't accept power.

    I've already done this, feeding both with a single balun and transmission line. Good match on both. The resulting network Z would only be 25 Ohms if each antenna was actually 50 Ohms, but that's not the case at all: The non-resonant antenna Z is very high. This is really like building a "parallel dipole" (which many call a "fan dipole"), with multiple dipole elements all fed in parallel.

    If they're oriented 90 degrees to each other, you can mount them just a few inches apart and use a very short jumper between them.
     
  7. W0AAT

    W0AAT XML Subscriber QRZ Page

    Might have to measure it mounted to see what actual feed impedance is going to be... I know there is some interaction even mounted 90 degrees to each other... forget what article it was in and what magazine but it has been done. And I have been tossing about doing the same. A hex beam is an option but winds/ice here and wire antennas are not a good match.
     

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